But this is the first time Apple has issued outright rejections for using UDIDs.

“Everyone’s scrambling to get something into place,” said Victor Rubba, chief executive of Fluik, a Canadian developer that makes games like Office Jerk and Plumber Crack. “We’re trying to be proactive and we’ve already moved to an alternative scheme.” Rubba said he isn’t sending any updates until he sees how the situation shakes out in the next few days.

For those unaware, the UDID is an alphanumeric string that is unique to each Apple device. It’s currently used by mobile ad networks, game networks, analytics providers, developers and app testing systems, like TestFlight, for example.

Playhaven, which helps developers monetize more than 1,200 games across iOS and Android, said several of its customers had been rejected in the last week. The company’s chief executive Andy Yang says that developers should try and stay as flexible as possible by supporting multiple ID systems until there’s a clear replacement.

“This is definitely happening,” Yang said. “In the next month or two, this is going to have an impact on all ad networks and apps using advertising. Everybody’s trying to make their own choices about what to use instead.”

At least one of the apps that faced issues a week ago came from a publicly-traded, multibillion dollar company, I confirmed. But they declined to be named so as not to jeopardize their relationship with Apple.

So here’s what I’m hearing. Two of the 10 review teams started doing blanket rejections of apps that access UDIDs this week. Next week, that will rise to four the ten teams, and keep escalating until all 10 teams are turning down apps that are still using UDIDs.

This is a big deal because mobile ad networks use these ID numbers to make their advertising better targeted. Using UDIDs, mobile ad networks can track consumers from app to app to understand more about ads they respond to and apps they use most often.

“The UDID is essential for managing the conversion loop,” said Jim Payne, who runs a real-time bidding platform for mobile ads called MoPub and was early at leading mobile advertising network AdMob before it sold to Google for $ 750 million. “All the performance dollars that are spent on mobile are going to impacted by this not being there.”

Yang and others are seeing a few developers get through approval process if they ask users for permissions first before storing their UDIDs. If so, this mirrors the approach that Facebook and Google Android take in making developers show a permissions dialog to consumers when they first install the app.

However, Yang’s not so sure that this is a good user experience or that enough consumers will say yes to make this strategy effective.

“I just don’t think the opt-in rate will be that high,” he said. “It feels like a Band-Aid solution for now.”